The invention relates to an adjusting device for a disc brake and, in particular, an adjusting device for a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle of the disc brake.
Adjusting devices or wear adjustors for disc brakes exist in various embodiments. DE 10 2004 037 771 A1 (having U.S. published counterpart application US2009/209890 A1) discloses an adjusting device for a disc brake, the specifications of which are expressly incorporated by reference herein. This adjusting device is suitable for a pneumatically actuated disc brake, in particular one of sliding-caliper design. Furthermore, the adjusting device can, however, also be used in pneumatically actuated fixed-caliper or pivoting-caliper disc brakes.
Pneumatically actuated disc brakes have over time become standard equipment on heavy commercial vehicles. Such disc brakes require mechanical boosting or “force multipliation” in order to produce the demanded brake application force, because the force of the pneumatically charged brake cylinders is restricted on account of the pressure level (at present approximately 10 bar) and the limited structural size of the brake cylinder. Presently known pneumatically actuated disc brakes have boost ratios of between 10:1 and 20:1. The piston strokes of the brake cylinders are in the range from 50 mm to 75 mm, resulting in brake application travels of approximately 4 mm for pressing the brake pads against the brake disc.
The friction material thickness of the brake pads lies in the range of 20 mm, and because two pads are installed, this results in a wear travel of approximately 40 mm, not taking disc wear into consideration. This travel is a multiple greater than the abovementioned brake application travel. It is therefore necessary for the brake to be adjusted correspondingly to the pad wear by means of a device. The prior art provides automatic wear adjustment by means of which the so-called air play, that is to say the gap between the brake pads and the brake disc in the non-actuated state, is kept constant independently of the wear state and wear behavior of the brake pads.
In commercial vehicles, use is very often made of disc brakes which have an adjuster which is arranged concentrically in the cavity of a threaded spindle and which is driven eccentrically by a rotary brake lever via a drive element (for example shift finger, toothed wheel). During a braking process, the rotary lever which is coupled to the piston rod of the brake cylinder performs a rotational movement. Before the rotational movement of the lever is introduced into the adjuster via the coupling mechanism of the adjusting means (for example shift fork and shift finger or toothed wheels), a so-called idle travel must be overcome. This travel is decisive of the size of the so-called air play, because during the movement, the adjustment is not activated, and the brake application travel therefore constitutes the air play. After the idle travel is overcome, the adjuster is set in a rotational movement, and an adjusting process is initiated by the coupling to the threaded spindle or tube.
DE 10 2004 037 711 A1 describes an adjuster of this type, which is shown in FIG. 5. The adjuster is composed substantially of the following functional elements: shaft 2; bearing disc 3; axial bearing 5; collar bush, or spacer sleeve 19; shift fork, or drive ring 6; ball ramp clutch 7; cone clutch 17; and cylindrical spring 12. With regard to the description, reference is made to DE 10 2004 037 711 A1.
An important element of the adjuster is the directional clutch. This function is realized by the interaction of the ball ramp clutch 7 and the cone clutch 17.
A rotational movement is introduced by the rotary lever into the shift fork with the drive ring 6, and into the ball ramp clutch 7 of the adjuster. The axial force hereby produced in the ball ramp clutch 7 generates, in the cone clutch 17, a friction moment which is dependent on friction coefficient, taper angle and friction radius.
In order that slipping of the cone clutch 17 does not occur, it is necessary, as in all friction-dependent freewheel systems, for the self-locking condition to be met, that is to say the generated friction force or generated friction moment must be greater than the clutch force or clutch torque to be transmitted:Mcone clutch>Mramp clutch 
During the course of development, it has been found that designing the cone clutch 17 within the given boundary conditions is highly problematic.
In order to provide a reliable clamping action even with very low friction coefficients (approx. 0.07) in the cone clutch 17, it is necessary for the cone clutch 17 to be designed with a relatively steep taper angle αK. The problem here is the release behavior in the axial direction. During relatively long periods of operation, it may occur that the cone clutch 17 no longer releases when relieved of load, and that as a result, the freewheel function is no longer provided.
It is therefore the object of the present invention to provide an adjusting device with a cone clutch, with the above disadvantages being eliminated or significantly reduced, and further advantages being obtained.
This and other objects are achieved by an adjusting device for adjusting for wear of the brake pads and the brake disc of a pneumatically actuated disc brake having a rotary-lever-actuated brake application device, which adjusting device can preferably be inserted into an adjusting spindle of the disc brake. An axial bearing is formed axially on one side of a drive ring and a ball ramp clutch with freewheel function is formed axially on the opposite side of the drive ring. The ball ramp clutch has balls, a drive bush arranged at the drive input side axially between the axial bearing and the balls thereof and a drive-output-side clutch ring. A cone clutch is arranged between the drive-output-side clutch ring and a spring sleeve for a cylindrical spring. The cone clutch has the drive-output-side clutch ring and a tapered bush which is connected to the spring sleeve. Clamping balls are arranged between the drive-output-side clutch ring and the tapered bush.
The cone clutch is equipped with clamping balls. By means of the clamping balls, it is obtained that the inner tapered bush can move in the axial direction without significant frictional locking on account of the rolling movement of the balls. As a result of the mounting of the balls in axially running longitudinal grooves, it is obtained that, in contrast, a friction-based blocking action is provided in the tangential direction.
This design offers the following advantages:
(1) correct release behavior in the axial direction even with very small taper angles;
(2) high friction action in the tangential direction;
(3) as a result of the mounting of the balls in grooves, linear contact, and therefore relatively favorable Hertzian stress, is provided between the balls and counterpart surface;
(4) cost-effective production of the parts by means of non-cutting shaping technology; and
(5) installation-space-saving design.
In one embodiment, it is provided that the tapered bush has an external profile which corresponds to an internal profile of the spring sleeve for a rotationally conjoint connection. This permits simple assembly, with a positively locking rotational connection being provided at the same time.
In an alternative embodiment, the tapered bush and the spring sleeve may be formed in one piece, as a result of which the number of parts, and assembly times, can be reduced.
In a further embodiment, it is provided that the axial bearing is formed by one side of the drive ring, by rolling bodies and by a collar of a collar bush which extends axially through the ball ramp clutch. This likewise reduces the number of different parts, and provides a compact design.
It is also provided that one end of the collar bush which extends through the ball ramp clutch forms, directly or via a thrust washer, an axial stop for the tapered bush. In this way, it is made possible for the axial bearing and ball ramp clutch to be assembled and held together in a simple manner, and minimal play of the axial bearing and ball ramp clutch is maintained.
A disc brake, in particular pneumatically actuated disc brake, has an adjusting device according to the above description.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.